Proglacial methane emissions driven by meltwater and groundwater flushing in a high Arctic glacial catchment

Abstract. Glacial groundwater releases geologic methane in areas of glacier retreat on Svalbard, representing a large, climate-sensitive source of the greenhouse gas. Methane emissions from glacial melt rivers are known to occur in other regions of the Arctic, but such emissions have not yet been considered on Svalbard. Over two summers, we monitored methane concentrations in the proglacial groundwater springs and river network of a 20 km2 valley glacier in central Svalbard to estimate melt season emissions from a single catchment. We found that methane concentrations in the glacial river reach up to 3170 nM, which is nearly 800-times higher than the atmospheric equilibrial concentration. We estimate a total of 1.0 ton of melt season methane emissions from the catchment, of which nearly two-thirds are being flushed from the glacier bed by the melt river. These findings provide further evidence that terrestrial glacier forefields on Svalbard are hotspots for methane emissions, with a climate feedback loop driven by glacier melt. As the first investigation into methane emissions from glacial melt rivers on Svalbard, our study suggests that summer meltwater flushing of methane from the ~1400 land-terminating glaciers across Svalbard may represent an important seasonal source of emissions. Furthermore, glacial melt rivers may be a growing emission source across other rapidly warming regions of the Arctic.